The Lowell-based transportation company said it had net earnings of about $84 million in the fourth quarter of 2012, up 16 percent from $72.6 million a year earlier.

The firm said the increase was due largely to cost controls, a lower cost of borrowing and a growth in revenue. Total operating revenue was $1.34 billion in the fourth quarter, up more than 11 percent from $1.2 billion in 2011.

Operating income for the quarter was up 17 percent to $143.3 million and earnings per share were up 15 percent to 70 cents compared to 2011's fourth quarter.

For the year as a whole, the company's profits topped $310.3 million, up nearly 21 percent from 2011's roughly $257 million.